The invention relates to an optoelectronic synchro generator having at least one photoelectric circuit element consisting of a light source and a receiver and a removable cover.
Such prior-art synchro generators are used primarily with industrial sewing machines for the generation of signals representing specific needle positions whereby the sewing machine may then be stopped in such positions, such as needle down or needle up, and further operations such as threat cutoff may be initiated.
In such a synchro generator ("synchronizer") known, for example, from U.S. Pat. No. 3,683,294, the positioning of the parts carrying the optically effective surfaces requires the removal of a cover. In order that the sensitivity of the receivers not be impaired, adjustment must not take place in broad daylight or directly exposed to the light of a lamp illuminating a work position. This complicates positioning considerably.
The same problems arise with a synchro generator known from East German Pat. No. 52,049 where the top shaft of a sewing machine carries a cup-shaped part which serves as shutter and has at least one aperture. A light source projects into the cup-shaped part. Disposed radially relative to the cup-shaped part are receivers which form a part of an electric circuit. As the cup-shaped part revolves, a light beam impinges on one of the photoelectric receivers, thus generating a signal representing the position of the aperture, and hence the angular position of the shaft. The two photoelectric receivers are adapted to be displaced on their carriers, and the angular positions of the shaft represented by signals therefore are variable. Here, too, the receivers are fully exposed to stray light once a cover has been removed. Yet it is exactly for such adjustments that the operator needs good light.